This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-261294, filed Aug. 30, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a mobile radio terminal and automatic frequency control circuit for use in a mobile telephone terminal, portable telephone system or wireless LAN system using the CDMA scheme.
2. Description of the Related Art
A receiving system of a conventional mobile radio terminal device in a CDMA-type radio communication system is constituted as shown in FIG. 1.
A radio signal from a base station (not shown) is downconverted to a baseband signal by a receiving unit (RX) 103. The baseband signal is output to a searcher 10 and fingers 31 to 3n. 
The searcher 10 detects number n of different passes suitable for reception by despreading the baseband signal at various timings. Then the searcher 10 assigns synchronous positions of slots and frames for reception of the respective passes to the fingers 31 to 3n as pass synchronization information.
Each of the fingers 31 to 3n generates a scramble code of the timing based on the pass synchronization information assigned by the searcher 10 and despreads the baseband signal by using the scramble code. Thus, n baseband signals despread by the fingers 31 to 3n are RAKE-synthesized.
The fingers 31 to 3n also have a function of detecting frequency errors xcex94f1 to xcex94fn of the passes assigned to themselves, in the results of the despreading, and is constituted as shown in FIG. 2.
The baseband signal from the receiving unit 103 is input to a multiplier 310. The multiplier 310 multiplies the baseband signal by a scramble code generated by a CPICH scramble code generator 320. The CPICH scramble code generator 320 has generated the scramble code at a timing based on the pass synchronization information assigned by the searcher 10.
The result of multiplication of the multiplier 310 is integrated during a period equivalent to 1 symbol by an integrator 330. The result of the integration is output to a 1-symbol delay unit 340 and a multiplier 360.
The 1-symbol delay unit 340 delays the result of integration of the integrator 330 for a period equivalent to 1 symbol and outputs it to a complex conjugate unit 350.
The complex conjugate unit 350 inverts a code of a complex component in the result of integration which is input from the 1-symbol delay unit 340 and outputs the result of the inversion to the multiplier 360.
The multiplier 360 obtains an amount of phase rotation in successive symbols, i.e. frequency errors (xcex94f1 to xcex94fn), as shown in FIG. 3 by multiplying the outputs of the integrator 330 and complex conjugate unit 350, which are shaped in a complex number.
The frequency errors xcex94f1 to xcex94fn obtained by the respective fingers 31 to 3n in the above-mentioned manner are added in an adder (xcexa3) 4. The result of the addition is averaged by a low-pass filter (LPF) 5 and output to a tanxe2x88x921 circuit 6 as the frequency error xcex94f.
The tanxe2x88x921 circuit 6 obtains an arc tangent component of the frequency error xcex94f. The arc tangent component is integrated by an integrator 7 and output to a VCO control conversion table 8.
The VCO control conversion table 8 stores voltage values corresponding to various values that are input from the integrator 7 and outputs the information of voltage values corresponding to the output values of the integrator 7. The voltage value information that is output from the VCO control conversion table 8 is converted to a voltage signal corresponding to the information by a D/A converter (D/A) 9.
The voltage signal obtained in this manner is used as a control signal of a voltage control oscillator inside a synthesizer 104. Thus the oscillation frequency of the voltage control oscillator is controlled so that the output (frequency error xcex94f) of the low-pass filter 5 can be zero.
Incidentally, recently, transmission diversity has been conducted at the base station. The base station comprises two transmission antennas ANT1 and ANT2 for transmission to the mobile radio terminal apparatus, and the transmission diversity allows the phase between the signals transmitted from the antennas to be controlled at the base station so that the signals can be in a proper condition in the mobile radio terminal apparatus.
Symbols of patterns shown in FIG. 4 (hereinafter xe2x80x9cAFC control symbolsxe2x80x9d) are transmitted in a 15-frame cycle from the transmission antennas ANT1 and ANT2, for the automatic frequency control (AFC) in the mobile radio terminal apparatus. The symbol patterns of FIG. 4 are examples according to 3GPP (3rd Generation Partnership Project).
FIG. 5 shows parts of the patterns of the AFC control symbols. In the pattern of the symbols transmitted from the transmission antenna ANT 1, all the symbols are xe2x80x9cAxe2x80x9d (A=1+j). In the pattern of the symbols from the transmission antenna ANT 2, xe2x80x9cAxe2x80x9d, xe2x80x9cAxe2x80x9d, xe2x80x9cxe2x88x92Axe2x80x9d and xe2x80x9cxe2x88x92Axe2x80x9d are repeated. xe2x80x9cxe2x88x92Axe2x80x9d indicates xe2x88x921xe2x88x92j.
If the transmission from the transmission antennas ANT1 and ANT2 to the mobile radio terminal apparatus is conducted at the same channel, a 0-th symbol as shown in FIG. 5 is xe2x80x9cAxe2x80x9d at both the transmission antennas ANT1 and ANT2 and thus becomes as shown in FIG. 6.
The first symbol in FIG. 5 is xe2x80x9cAxe2x80x9d at the transmission antenna ANT1 and xe2x80x9cxe2x88x92Axe2x80x9d at the transmission antenna ANT2. Therefore, the transmitted signal becomes a signal whose signal amplitude is almost zero as shown in FIG. 6.
For this reason, even if the conventional circuit as shown in FIG. 2 obtains the phase differences between symbols xcex94xcex801, xcex94xcex812, xcex94xcex823, xcex94xcex834, xcex94xcex845, . . . , in accordance with the signals transmitted from the base station which conducts the transmission diversity in order to obtain the frequency error xcex94f from the phase differences, the circuit cannot detect the frequency error xcex94f or normally execute the frequency-locking operation under the condition as shown in FIG. 6 or the condition that, particularly, the frequency error xcex94f is great as seen when the power supply is turned on.
That is, if the communication partner executes the transmission diversity, the conventional automatic frequency control circuit cannot detect the frequency errors under the condition that, particularly, frequency error xcex94f is great as seen when the power supply is turned on and, therefore, cannot normally execute the frequency-locking operation.
The present invention aims to provide a mobile radio terminal and automatic frequency control circuit capable of executing a normal frequency-locking operation regardless of whether or not the communication partner executes the transmission diversity.
To achieve this object, there is provided a mobile radio terminal and automatic frequency control circuit comprising: symbol pattern storing means for storing patterns of symbols transmitted to allow a communication terminal to execute transmission diversity; synchronous information detecting means for detecting synchronous information of slots and frames of the signal received from the communication terminal, in the baseband signal; despreading means for despreading the baseband signal; integrating means for integrating a result of the despreading of the despreading means; integration controlling means for controlling the integrating means, to allow the integrating means to integrate the result of despreading of the despreading means corresponding to two successive predetermined periods in which combinations of the symbols are the same, in each of the predetermined periods, in accordance with the synchronous information detected by the synchronous information detecting means and the symbol patterns stored in the symbol pattern storing means; delay means for delaying an output of the integrating means; frequency error detecting means for detecting a frequency error of the local oscillation signal in accordance with a phase difference between a delay output of the delay means and an output of the integrating means; and frequency controlling means for controlling the frequency of the local oscillation signal in accordance with the frequency error detected by the frequency error detecting means.
In the above-constituted mobile radio terminal and automatic frequency control circuit, the integrating means is controlled to integrate the result of despreading of the despreading means corresponding to two successive predetermined periods in which combinations of the symbols are the same, in each of the predetermined periods, in accordance with the synchronous information detected by the synchronous information detecting means and the symbol patterns stored in the symbol pattern storing means. The frequency error of the local oscillation signal is detected in the phase difference between the output of the integrating means and the delayed output thereof to control the frequency of the local oscillation signal.
According to the mobile radio terminal and automatic frequency control circuit, even if the communication terminal transmits executes transmission from a plurality of transmission antennas to its own station by the transmission diversity, the reception signals are integrated in a period in which the combinations of the symbols transmitted from the respective transmission antennas are the same as one another and the frequency error is detected in accordance with the phase difference in the result of the integration. Accordingly, the frequency error can be exactly detected and the frequency-locking operation can be normally executed, regardless of whether or not the communication partner executes the transmission diversity.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.